Expert: Kevin Pilotte - 4/1/2004

Question
Sir, I've owned a 1970 american motors amx since 1982. It's a 390 automatic that I bought from original owner. The orginal owner blew the motor shortly after buying it, and replaced the block with a 401 block. If I'm not mistaken he told me he used 390 crank,now my question. I have the borg warner tranny, is it possible to put a 904 Chrysler in this vehicle with a 390 crank? If I were to pull the tranny is there a way to tell by measuring the end of crankshaft which one I have? The reason I don't pull the motor is I had it rebuilt in the mid-eighties and it has less than 5000 miles on it and runs beautifully, except for a wimpy shifting tranny. If it is possible to put the Chrysler in do you know of any places that sell complete rebuilt transmissions without a core?

Answer
If your engine has a crank from a 390, it will have to be modified before installing a 727. It involves machining the rear of the crank to allow installation of an adapter. The adapter p/n was 3216130. AMC started using Torque-Commands (Mopar)in 1971, so any engine crankshaft earlier than that requires modification. I would recommend a 727, not a 904. The 904 came behind 6 cylinders.I would contact an AMC vendor like American Performance in Cocoa,FL or Eddie Stakes in Houston for transmission leads. There is an old AMC book available in reprint called "Performance American Style". It shows in detail the machining necessary to upgrade your trans. Good Luck.
Kevin.